With improvement in high performance of a photographing lens such as a zoom lens unit which is capable of changing the focal distance and in downsizing according to the user's demand as to an image pickup apparatus such as a digital camera, there are increasing types of image pickup apparatus employing a so-called collapsing photographing lens unit in which lens cylinders are collapsed within a body of the image pickup apparatus when photographing is not carried out. Furthermore, since not only a simple reduction in dimensions but also a further reduction in a thickness of the image pickup apparatus are also demanded, it is now important to reduce the thickness of the lens barrel portion in a collapsed state.
As a technology to cope with the demand for reduction in the thickness of the image pickup apparatus, a construction has been used, in which the lens cylinders are collapsed into the body of the image pickup apparatus when the photographing is not carried out and in which a part of the lenses is evacuated from an optical axis of the lenses in photographing, when the lens cylinders are collapsed. Such a technology is disclosed, for example, in JP-A 2003-315861 and in JP-A 2003-149723. According to the structures disclosed in these Japanese unexamined patent application publications, since a part of the lenses is evacuated from the optical axis when the lens cylinders are collapsed, the dimension of the entire lenses in a direction of the optical axis can be reduced in the collapsed state, so that the thickness of the image pickup apparatus can be reduced.
However, in the structures disclosed in JP-A 2003-315861 and JP-A 2003-149723, the position of the lens evacuated from the optical axis is substantially within that lens cylinder which has the maximum outer diameter. Therefore, the lens cylinders contribute to reduction in thickness of the image pickup apparatus when the lenses are collapsed, but the outer diameter of the lens barrel increases. When compared with a case where the lens is not evacuated from the optical axis, since the outer diameter of the lens cylinders increase, the dimensions of the lens cylinders, in particular, the dimensions of the lens cylinders as viewed in a plane orthogonal to the optical axis increase. As a result, there is a problem that the dimensions of the image pickup apparatus, in particular, the dimension as viewed from a front side of the image pickup apparatus increases.